Plain radiographs obtained in 25 patients with acute anterior cruciate ligament (ACL) tears detected with magnetic resonance imaging were retrospectively evaluated to identify associated bone lesions. Fracture of the posterior part of the lateral tibial plateau (LTP) was seen in 11 patients, impacted fracture of the lateral femoral condyle (LFC) in two, lateral tibial rim fracture (Segond fracture) in three, and avulsion fracture of the tibial attachment of the ACL in two. The latter three fractures have been associated with an ACL tear. Conversely, fractures of the posterior part of the LTP have not been associated with ACL tear and are recognizable on plain radiographs. Impaction of the LFC on the LTP and avulsion of the posterior tibial capsular junction may account for the association of the fracture of the LTP with the acute ACL tear. This type of fracture represents the most frequent indirect sign of ACL tear seen on plain radiographs.

In all cases, low-and high-signal masses were observed on Ti-and T2-weighted images, respectively. The cysts were unilocular with a sharply defined margin, ranging from 0.5 to 3.0 cm in diameter. The thin wall was of low signal intensity on T2-weighted images. Our experience suggests that MR imaging is useful in demonstrating the liquid content of prostatic and seminal-vesicle cysts and in establishing their size and location.

The aims of the study were to determine the frequency of visualization of the normal transverse geniculate ligament (TGL) of the knee on lateral plain radiographs with magnetic resonance imaging (MRI) as a reference, and to determine features that make this ligament apparent on plain radiographs. 50 consecutive lateral plain radiographs and sagittal T1-weighted images of corresponding knees were evaluated prospectively. A TGL was considered visualized on plain radiographs when an opacity of soft-tissue density was apparent in the posterior part of the Hoffa's fat pad. The TGL was identified in 29 of the 50 (58%) sagittal MR images; a TGL was observed on the lateral plain radiographs of six patients (12%). Correlation with the MR images showed that, when visualized on plain radiographs, the ligament is at least 3 mm thick and completely surrounded by fat. Our study shows that the TGL is a normal variant that can be recognized frequently on lateral plain radiographs of the knee.

Visualization of the transverse geniculate ligament of the knee in four patients is described. This normal variant was seen on lateral plain radiographs as a small, rounded opacity surrounded by fatty tissue and located anterior to the knee joint. Magnetic resonance imaging helped confirm this image to be that of the transverse geniculate ligament.

Magnetic resonance imaging (MRI) of an irreducible knee dislocation can help physicians evaluate associated bone and ligamentous lesions. However, caution should be taken when interpreting the images because the capsuloligamentous interposition seen in irreducible knee dislocations may be misdiagnosed as a meniscal lesion.